1. Field of the Invention
This invention relates to bags having a weakened portion and more specifically to bags which suddenly and fully rupture at a predetermined force.
2. Description of the Prior Art
It is common practice for a centrifuge to be used in many of the standard assay and analysis procedures presently employed by medical laboratories, testing and research facilities. The most frequent use of a centrifuge is for the separation of the chemical components of a sample where the components have different specific gravities. However, it is also common to use a centrifuge to thoroughly mix reagents with a sample or to otherwise combine the components of a mixture. In this regard it is sometimes necessary to introduce reagents into a sample mixture while the sample is being centrifuged. This has proven very difficult to do for the obvious reason that the sample is generally rotating in a centrifuge at a high rate of speed at the very time that the reagents are to be introduced. The solution to this has been to find alternative, but generally less preferred, steps in the process for introducing the reagents when the sample is more conveniently accessible.
However, by using the release bag of this invention, it is possible to conveniently and accurately disperse a reagent or reagents into the test chamber of a cuvette and to mix reagents with a sample while the sample is being centrifuged. The centrifuged release bag has a single seam which is weaker than the remaining walls and seams and which is designed to suddenly and fully rupture within a predetermined range of centrifugal force (or within a predetermined range of revolutions per minute or r.p.m.). The idea of inserting a centrifugal release bag in a cuvette and having the bag burst during centrifugation has been previously disclosed in commonly assigned U.S. Pat. No. 3,713,775 (1973) to Schmitz. Other known burstable bags are included in U.S. Pat. No. 3,478,871 (1969) and U.S. Pat. No. 3,601,252 (1971) both to Sager. The bag of this invention is equally adaptable to bursting by means of manual pressure. While this disclosure will primarily be directed to a bag designed to release a substance during centrifugation, it should be understood that the same bags that are centrifugally burstable are likewise manually burstable. Therefore, for purposes of this application, the terms centrifugal release bag and burst bag should be considered interchangeable.
Prior attempts at making reagent bags having a single weakened seam have generally resulted in a bag which does not have the desired degree of predictability in terms of the r.p.m. at which the contents are released and additionally have generally suffered in that the process of making the bags made it difficult to prevent contamination of the reagent bag itself. One prior method of making such a bag was to place two strips of a plastic material together and to seal the strips with wax using less wax at one seam. Problems have been found in this method due to the fact that the wax was generally contaminated and due to the fact that the heat which may be developed during centrifugation creates a tendency for the seams of the bag to entirely disintegrate, thus prematurely releasing the reagents contained therein. In addition, the range of reagents that could be put into bags was not large due to the chemical reactivity between the wax and most chemical reagents. A second pair method of weakening a single portion of a reagent bag was by the use of a simple cutting instrument, such as a razorblade, to make a small cut in the bag material at the desired rupture point. This has obvious deficiencies in that it ruptures the use of a cutting blade on a structure which is generally approximately 0.003 inches thick. The cut required in something such as this is on the order of 0.0025 inches deep into the 0.003 inch structure. This has created many problems which have not been solved by the use of a manual or automatic cutting instrument or a blade cutting instrument in the making or forming of centrifugal release bags. Cutting the material with a knife blade also results in metal flakes remaining in the material and forms a score which may have capillary leaks when the material is folded to form the bag. The use, however, of a laser has been very successful in forming the linear depression necessary in forming the reagent bags of this invention. More particularly, the use of the laser allows not only a cut to be made but also the size and shape of the cut to be varied by varying the focal length of the laser beam. Additionally, modern technology allows the control of the strength of the laser beam to whatever degree is desired and hence the cut or linear depression made into the film can be controlled to the desired degree to allow bags to be manufactured having bursting points over a wide spectrum of centrifugal forces.